Study On The Reduction Of Unsaturated Ketones Catalyzed By Titanium(?)

?,?-enone structural units are not only widely existed in natural products,medicines,fine chemicals,etc,but also used in various organic transformations as synthetic intermediates,therefore,their synthesis research has always attracted much attention from synthetic chemists.The 1,4-selective reduction of ?,?-alkynones is an important strategy for the preparation of corresponding enones,but it is still a very challenging subject due to shortcomings,such as easy over-reduction,dependence on precious metals,and difficulty in recycling.In view of the fact that the catalytic application of cheap metal titanium(?)complexes,function through single-electron-transfer(SET)reduction mechanism,has shown its capability in the activation of organic functional groups such as epoxy compounds,aldehydes,ketones,halogenated hydrocarbons,etc,combined with our group's research basis in the synthesis and catalysis of titanocene complexes and molecular sieves,this thesis aims to solve the selective reduction problem of ?,?alkynones and the recovery problem of titanocene(?)catalysts,and through ligand control and molecular sieves immobilization strategies,the selective reduction of ?,?alkynone and the immobilization of the titanocene(?)catalytic system has been realized.At the same time,the reaction mechanism was systematically explored by in-situ NMR,EPR,MS,kinetics,XRD,TEM and other research methods.The main content and the results obtained are as follows:(1)The strategy of ligands' control of titanocene(?)complexes developed a new method for the selective catalytic reduction of ?,?-alkynes to(E)-?,?-enone derivatives,and 24 kind of target molecules has been successfully synthesized under mild reaction conditions,with the separation yield up to 88%,and the enone/alkanone selectivity exceeds 99:1.The reaction mechanism was thoroughly explored using in-situ EPR,HRMS,NMR,isotope tracking,kinetic experiments and other related methods,and possible reaction mechanisms were proposed based on the mechanism research results.The conclusions include:EPR results show that Et3N·HCl helps the formation of mononuclear titanocene(?)catalytic species from Cp*2Ti(?)Cl2,and the formed titanium(?)species can effectively coordinate with the alkynone substrate;HR-MS studies show that the stable radical tetra-methylpiperidine nitroxide(TEMPO)successfully captured the allene radical/propargyl radical intermediate,indicating that the reaction proceeds through the free radical mechanism;isotope experimental studies show that Et3N·HCl is the actual hydrogen donor,and the donating step is not the rate-determining step;the reduction kinetics study of alkynone and its intermediate products shows that the reason for the generation of selectivity of enone/alkanone in the reaction may be attributed to the formation of zinc allenide intermediates.(2)Aiming at the hydrogenation reduction reaction of chalcone catalyzed by lowvalent titanocene,Ti-USY(Ultra-Stable Y zeolite)heterogeneous catalyst with catalytic activity equivalent to Cp2TiCl2 was prepared by immobilizing titanocene dichloride on molecular sieves,the recycling of the catalyst was realized,and 16 dihydrochalcone compounds was also synthesized,with the highest separation yield at 98%.Cyclic voltammetry was used to study the oxidation-reduction properties of the catalyst,and it was found that Ti-US Y was easier to be reduced than unsupported Cp2TiCl2.The catalytic activity of Ti-USY before and after catalysis was systematically studied,the analysis of XRD and TEM show the TiOx in lower oxidation state that actually plays a catalytic role in the process of multiple cycles.Using NMR analysis,it was determined that the hydrogenated protons in the products originated from Et3N·HCl,through the isotope tracking method.This work provides a basis for the construction of a sustainable catalytic system for low-valent titanium.